This invention relates to agents for reducing the fluidity drop of hydraulic cement compositions (herein simply referred to as "the fluidity drop reducing agents") and methods of producing such agents, as well as methods of reducing the fluidity drop of hydraulic cement compositions. More particularly, this invention relates to agents which are capable of reducing the drop in the fluidity with time (herein referred to as "the slump loss") of hydraulic cement compositions such as cement pastes, cement grouts, mortars and concrete and methods of producing such agents, as well as methods of reducing the fluidity drop of such hydraulic cement compositions.
Many kinds of cement dispersant are being used for improving the fluidity of hydraulic cement compositions. If a cement dispersant is used to prepare a hydraulic cement composition with a highly reduced water content, however, its slump loss becomes too great, giving rise to the problem of poor workability and applicability. In order to reduce the slump loss, therefore, it has been proposed to use a water-soluble vinyl copolymer, which itself has the property of reducing the slump loss, as the cement dispersant. Examples of such water-soluble vinyl copolymer include (1) those obtained by co-polymerizing (meth)acrylates (as disclosed in Japanese Patent Publication Tokkai 1-226757, U.S. Pat. No. 4,962,173, and Japanese Patent Publication Tokkai 4-209613); and (2) copolymers of maleic anhydride and alkenyl ether and their derivatives (as disclosed in Japanese Patent Publications Tokko 58-38380, Tokkai 63-285140 and Tokkai 2-163108 and European Patent Publication 537872). These prior art methods of using such a water-soluble vinyl copolymer as the cement dispersant, however, are not capable of sufficiently reduce the slump loss. In order to further reduce the slump loss, therefore, there have also been proposals to use a so-called fluidity drop reducing agent in addition to a cement dispersant. According to a method of this kind, as disclosed in Japanese Patent Publication Tokko 5-67579, a water-insoluble copolymer obtained from maleic anhydride and olefin is used together with a cement dispersant, and the slump loss is reduced by making use of the property of this water-insoluble copolymer to undergo hydrolysis by a basic hydroxide generated by the hydration reaction of the cement and to thereby gradually become a water-soluble copolymer. This prior art method of using a fluidity drop reducing agent together with a cement dispersant, however, is not advantageous because the ability to reduce the slump loss varies and becomes weaker with time and also because the setting retardation is large.